Hydrofluorocarbons and hydrochlorofluorocarbons are known in the art to be useful in a variety of industrial applications including blowing agents, refrigerants, sterilant gases and solvent applications. While chlorofluorocarbons (CFCs) are known for similar applications, they are believed to be deleterious to the earth's protective ozone layer and it has been desired to develop substitutes which are essentially not ozone depleting. Several such replacement materials have been developed. These include 1,1-dichloro-2,2,2-trifluoroethane (HCFC-123); 1,2-dichloro-1,2,2-trifluoroethane (HCFC-123a); 1-chloro-1,2,2,2-tetrafluoroethane (HCFC-124), 1-chloro-1,1,2,2,-tetrafluorochloroethane (HCFC-124a) and pentafluoroethane (HFC-125). It is expected that the demand for these latter materials will increase dramatically in the future and hence commercially viable processes for their preparation are desired. Many processes for the production of HCFC's and HFC's are known in the art. Typically these processes involve a fluorination using catalysts which have a very short life span and hence they are impractical for commercial application.
U.S. Pat. No. 3,258,500 describes a process for fluorination of halogenated alkanes and alkenes using a gel-type activated chrome oxide catalyst. HCFC-124 and HFC-125 are produced by reacting tetrachloroethylene with anhydrous hydrogen fluoride in the presence of an anhydrous chromium oxide on alumina fluorination catalyst. Catalyst life or stability is not discussed but the process has a low selectivity and yield. U.S. Pat. No. 4,843,181 describes a gas phase process which reacts tetrachloroethylene with hydrogen fluoride in the presence of chromium oxide made from a pyrolysis of (NH.sub.4).sub.2 Cr.sub.2 O.sub.7. Catalyst stability is not mentioned. This method is disadvantageous since an extremely long contact time is required between the catalyst and the reactants. U.S. Pat. No. 4,967,023 discloses a process which hydrofluorinates perchloroethylene (PCE) with a chromia on AlF.sub.3 catalyst. A low conversion of reactants is reported. U.S. Pat. No. 3,755,477 describes an improved chrome oxide catalyst for fluorination of PCE at 360.degree. C. but no catalyst life or stability are reported. Similar processes and low yields are described in U.S. Pat. No. 4,766,260. The gas phase conversion of perchloroethylene to other HCFC's is shown in U.S. Pat. No. 5,091,601. U.S. Pat. No. 5,155,082 describes a partially fluorinated aluminum/chromium oxide catalyst for the hydrofluorination of a halogenated aliphatic hydrocarbon to produce a chlorofluorocarbon, hydrochlorofluorocarbon or hydrofluorocarbon. According to this patent, when HCFC-124 is the desired hydrofluorocarbon the preferred starting material is HCFC-123 or HCFC-123a. HCFC-123 or HCFC-123a, preferably is produced from perchloroethylene as the starting material. None of these references suggest the use of a phenolic type inhibitor in the perchloroethylene.
Heretofore it has been a problem in the art to conduct a vapor phase fluorination of perchloroethylene with anhydrous hydrogen fluoride in the presence of a fluorination catalyst since the perchloroethylene tends to form an oxidation product during storage and transportation. This oxidation product is acidic in nature and forms within the perchloroethylene from atmospheric oxygen and hydrogen from atmospheric moisture. Apparently the perchloroethylene itself tends to break down and form a tarry or carbonaceous material. One proposed solution has been to transport and store the perchloroethylene under a nitrogen blanket. However, this makes handling impractical. Another solution has been to incorporate an amine oxidation inhibitor such as 4-methyl morpholine or diallyl amine in the perchloroethylene. However, such amines cause the fluorination catalyst to have a markedly reduced effectiveness after a relatively short time. Thereafter the fluorination process must be stopped and the catalyst either replaced or reactivated. Typical regeneration requires heating the catalyst to 350.degree. C. for about 12-24 hours. This causes a undesirable loss of production time. The process of this invention also concerns contacting a vapor mixture of perchloroethylene with anhydrous hydrogen fluoride in the presence of a fluorination catalyst. However, it has now been found that by the substitution of a small amount of a phenolic type inhibitor in the perchloroethylene that improved catalyst stability is noticed. In another embodiment of the invention, the inhibitor component is essentially completely removed prior to feeding the purged perchloroethylene to the fluorination reactor. Thus, the process has a more stable operation since the catalyst stability is improved and regeneration cycles are minimized. In practical terms, instead of having to regenerate the catalyst after one or two weeks of service, now several months of service can be expected before a regeneration is necessary. All inhibitors are believed to coke the catalyst, however, the phenolics have been found to do so to a much lesser extent. The result is a more economical process for producing hydrofluorocarbons and hydrochlorofluorocarbons, especially HCFC-123, HCFC-123a, HCFC-124, HCFC-124a, and HFC-125.